Safety system for fluorescent lamp ballasts



March 30, 1965 J. ca SOLA SAFETY SYSTEM FOR FLUORESCENT LAMP BALLASTSFiled Sept. 29, 1953 I I a nun I United States Patent 3,176,187 SAFETYSYSTEM FQR FLUQRESCENT LAMP BALLASTS Joseph G. Sola, River Forest, 111.,assignor, by mesne assignments, to Basic Products Corporation, WestMilwaukee, Wis, a corporation of Wisconsin Fiied Sept. 29, 1253, Ser.No. 382,903 2 Claims. (Cl. 315257) This invention relates to safetysystems for use in connection with ballasts for gaseous dischargedevices, such for example as fluorescent lamps, and it is an object ofthe invention to provide an improved system of this character.

Fluorescent lamps, as well as other gaseous discharge devices, require ahigh voltage for starting and a ballast for limiting the current throughthe device after it has started. The presence of the high startingvoltage is a hazard. Moreover, fluorescent lamps not infrequently aremore difficult to start than is normal, or the starting thereof may beerratic, due perhaps to temperature, pressure and humidity conditions,the presence of static charges on some portions of the lamps orsurrounding fixture, factors arising out of the distribution of staticciation with a metallic fixture has been found to be helpful as has alsogrounding that fixture.

The presence of a grounding connection with the ballast makes itpossible for a person standing on ground, for example, to come intocontact with the available high voltage by holding onto the terminals atone end of a fluorescent lamp out of its socket while the other end isbeing inserted into an appropriate socket. It has been found, at least,in the case of certain recent developments in fluorescent lamps, thatwhen one end of the lamp is inserted into the socket, and that socket isenergized, the lamp may actually break down and conduct, therebycreating a serious shock hazard to the person installing the lamp.Accordingly, it i a further object of the invention to provide in afluorescent lighting ballast, in

which a circuit component is required to be grounded, an improved safetysystem having no substantial shock hazard.

Further objects of the invention will become apparent as the descriptionproceeds and the invention may be better understood by reference to theaccompanying drawing, in which:

FIGURE 1 is a circuit diagram of a fluorescent lamp bal ast embodyingthe invention; and

FIG. 2 is a circuit diagram of another form of fluorescent lamp ballastembodying the invention.

Referring to the drawings, the invention is shown embodied in a ballast14 (shown enclosed in a broken line rectangle) for energizing a pair offluorescent lamps 11 and 12, for example, all of which may be mounted ina fluorescent lamp fixture 13 shown schematically by the broken linebearing this reference character. The fixture 13 is shown grounded,inasmuch as this is common practice in the lighting art.

The ballast it may be of the resonant type, such as is shown and claimedin the applicants prior Patent No. 2,346,621 for Alternating CurrentSupply System, granted on April 11, 1944, and includes a primary winding14, a secondary winding 15, and a core 16 upon which the primary andsecondary windings are disposed. The transformer is of the high leakagereactance type, the leakage 3,176,187 Patented Mar. 30, 1965 reactancebeing provided, for example, by means of a shunt 17 magneticallydisposed between the primary and secondary windings, and the primarywinding 14 is provided with a pair of leads 13 and 19 for connection toa suitable source of alternating voltage, for example, one hundred tenvolts and sixty cycles. The lead or conductor 1% may be designated as aground connection so that when the ballast is installed and connected,this conductor becomes connected to ground as shown, such being commonpractice in the lighting art for safety reasons and for improvingstarting of the lamps.

The secondary winding 15 is provided with a sufflcient number of turnswith respect to the primary winding, whereby the voltage available tothe fluorescent lamps 11 and 12 is suflicient to start them in sequenceand to operate them in series. The secondary winding 15, independentlyof electrical connection to the primary winding, provides the voltagefor starting and operating the fluorescent lamps 11 and 12 and isconnected in series with them through a circuit which may be traced asfollows: From the right end of secondary winding 15, through condenser21, conductor 22 to one of the terminal at the right end of fluorescentlamp 12, through the fluorescent lam-p 12, conductors 23 and 24 from theterminals at the left end of fluorescent lamp 12 to the terminals at theright end of fluorescent lamp 11, through the fluorescent lamp 11 andthrough conductors 25 and 26 to the left end of the secondary winding15. A condenser 27 is shown connected from conductor 22 to a conductor28 which, in turn, is connected to the conductor 23. By means of thecondenser 27 and its connections which place it across lamp 12, thevoltage of the secondary winding is applied to the fluorescent lamp 111at the starting instant, whereby the full voltage is applied tofluorescent lamp 11 and it starts. Thereafter, the current in condenser27 produces a suflicient voltage drop therein to strike fluorescent lamp12 and the two fluorescent lamps, then, operate in series across thesecondary winding, all as is well understood in this art. The condenser21 cooperates with the secondary winding 15 to provide a conditionapproximating series resonance as is described in the applicantsaforesaid patent.

Other forms of ballasts and starting arrangements may, of course, beprovided.

Three windings 29, 31 and 32 are wound coupled to the primary winding 14so as to have voltages induced therein. The winding 29 is shownconnected by means of conductors 25, 33 and 34 to the terminals at theleft end of fluorescent lamp 12. The winding 31 is shown connected bymeans of conductors 23, 28, 35, 36 and 24 to the terminals at the rightend of fluorescent lamp 11 and the terminals at the left end offluorescent lamp 12. The winding 32 is shown connected by means ofconductors 22, 37 and 38 to the terminals at the right end offluorescent lamp 12. The winding 29, 31 and 32 provide heating currentfor the filaments of the fluorescent lamps 11 and 12 and remainenergized while the lamps are operating.

Connected from the left end of Winding 15 to the conductor 19 is anauxiliary circuit means 39. Through this auxiliary circuit means,connected as indicated, the terminals at the left end of lamp 11 becomegrounded when the ballast is installed and the lamp is disposed in itssockets. By virtue thereof, it has been found that the fluorescent lampsstart with greater ease and do so consistently.

It has been found suflicient to ground any one of the terminals of thefluorescent lamps. Also the ground may be through any one of the circuitcomponents of the ballast. Moreover, the grounding connection may bemade internally of the ballast as shown in FIG. 1, or a separate leadmay be brought out for the purpose. In

some instances it may be sufiicient to make the grounding connection tothe fixture 13 and, for example, may be made through the metallic casewhich ordinarily surrounds the ballast itself..

The term ground as used in this application comprehends the earth aswell as any artificial ground, .such as a large metallic surface, forexample, a lamp fixture which may not be connected to earth.

A person standing on ground while the ballast is energized and graspingthe right end of fluorescent lamp 111 out of its socket, while the leftend is disposed in its socket, will be in no danger of shock since theleft end of. fluorescent lamp 11 is connected'to' ground throughconductors 25, 26, the circuit means 39, and conductor 19. The filamentat the left end of fluorescent lamp 11 is heated by winding 29 and thelamp is in condition to start when the proper voltage is appliedthereto. If the person grasps the left end of fluorescent lamp 11, acir- I cuit to ground may be traced through the fluorescent lamp,conductors 23 and 24, fluorescent lamp 12 and condenser 27 in parallel,conductor 22, condenser 21, secondary winding 15, circuit means 39 andconductor 19 to ground. If a person grasps the left end of fluorescentlamp 12, a circuit may be tracedto ground as follows: Throughfluorescent lamp 12, conductor 22, condenser 21, secondary winding 15,circuit means 39 and conductor 19 to ground. If a person grasps theright end of the fluorescent lamp 12, a circuit may be traced to groundas follows: Through fluorescent lamp 12, conductors 23, 28, condenser27, conductor 22, condenser 21, secondary winding 15, circuit means 39and conductor 19 to ground. In the latter three instances, thepossibility of shock to the person exists since the filaments of thelamps are heated by thewindings connected thereto. To eliminate thisshock hazard, the circuit means 39 may comprise a sufficiently highimpedance or resistance, for example of the order of one million ohms,which will limit any current flow in the circuits traced to a negligibleor non-hazardous value.

The circuit of FIGJ 2 is the same as that of FIG. 1 with the exceptionthat the auxiliary circuit means 39 is connected at one end to conductor36 instead of to conductor 26. fluorescent lamp 11, or the right end offluorescent lamp 12, is grasped by a person, no shock hazard existssince each of the other ends of these lamps is connected to groundthrough conductor 36, circuit means 39 and conductor 19. When the rightend of fluorescent lamp 11 is grasped, a circuit to ground may be tracedthrough fluorescent lamp 11, conductors 25 and 26, secondary winding 15,condenser 21, conductor 22, fluorescent lamp 12 in parallel withcondenser 27, conductor 36, circuit means 39, and conductor 19 toground. If the left end of fluorescent lamp 12 is grasped, a circuit toground may be traced through the fluorescent lamp 12, conductor 22,condenser 21, secondary winding 15, conductor 26, con ductor 25,fluorescent lamp 11, conductors 24 and 36, circuit means 39 andconductor 19 to ground. In these latter two instances, a shock hazardmay exist but the circuit means 39, having sufiicient impedance, forexample, a resistance of a million ohms as already indicated, thecurrent which may flow is reduced to a negligible or non-hazardousvalue. Other circuits to ground from the lamp terminals may perhaps befound but their shock hazard is also removed as described.

In this case, when either the left end of- The hazardous conditionsreferred to arise in part because the filaments of the lamps areenergized since the heating'windings are connected to the filamentswhenever the fluorescent lamp terminals are disposed in the appropriatesockets.

While the circuit means 39 havebeen shown connected at one end to aconductor 19, which'may be designated as a grounding connection, and inFIG. 1 the other end has been shown connected to conductor 26terminating in a ballast lead 25 and in FIG. 2 has been shown connectedto conductor 36 also forming a ballast lead, the circuit means 39 may beconnected to other components.

While particular embodiments of the invention have been shown, it willbe. understood, of course, that the invention is not limited theretosince many modifications may be made, and it is, therefore, contemplatedby the appended claims to cover any such modifications as fall withinthe true spirit and scope of the invention.

. The invention having thus been described, what is claimed and desiredto be secured by Letters Patent is:

1. Ballast means for use with fluorescent lighting tube means and agrounded source of AC. power, said ballast means comprising a circuitincluding a primary Winding for connection to said grounded source, acircuit including a secondary Winding for applying AC. voltage acrosssaid tube means, said primary and secondary windings being coupledmagnetically but isolated electrically, and high impedance auxiliarycircuit means connected between the circuit of said primary winding andthe circuit of said secondary winding whereby grounding of any point inthe circuit of said secondary winding will complete a circuit throughsaid primary winding circuit and including said auxiliary circuit means,the impedance of said auxiliary circuit means being suflicient to limitthe current therethrough to a value less than that creating a shockhazard.

2. Ballast means for use with fluorescent lighting tube across said tubemeans, said primary and secondary windincluding said auxiliary circuitmeans, the impedance of I said auxiliary circuit means being suflicientto limit the current therethrough to a value less than that creating ashock hazard, a circuit being established from ground through saidauxiliary circuit means, said secondary winding, the tube means and themetallic fixture to aid in initiating operation of the tube means.

References Cited in the file of this patent UNITED STATES PATENTSLemmers Apr. 18, 1950 Peterson i May 8, 1951 Ranney Nov. 10, 1953

1. BALLAST MEANS FOR USE WITH FLUORESCENT LIGHTING TUBE MEANS AND A GROUNDED SOURCE A.C. POWER, SAID BALLAST MEANS COMPRISING A CIRCUIT INCLUDING A PRIMARY WINDING FOR CONNECTION TO SAID GROUNDED SOURCE, A CIRCUIT INCLUDING A SECONDARY WINDING FOR APPLYING A.C. VOLTAGE ACROSS SAID TUBE MEANS, SAID PRIMARY AND SECONDARY WINDINGS BEING COUPLED MAGNETICALLY BUT ISOLATED ELECTRICALLY, AND HIGH IMPEDANCE AUXILIARY CIRCUIT MEANS CONNECTED BETWEEN THE CIRCUIT OF SAID PRIMARY WINDING AND THE CIRCUIT OF SAID SECONDARY WINDING WHEREBY GROUNDING OF ANY POINT IN THE CIRCUIT OF SAID SECONDARY WINDING WILL COMPLETE A CIRCUIT THROUGH SAID PRIMARY WINDING CIRCUIT AND INCLUDING SAID AUXILIARY CIRCUIT MEANS, THE IMPEDANCE OF SAID AUXILIARY CIRCUIT MEANS BEING SUFFICIENT TO LIMIT THE CURRENT THERETHROUGH TO A VALUE LESS THAN THAT CREATING A SHOCK HAZARD. 